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NOTE TO ED ITORS : T hi s f a c t s h e e t o u t l i n e s t h e m is si onand b a s i c s c i e n t i f i c r a t i o n a l e f o r Voyager. I t i s sug-g e s t e d t h a t it be r e t a i n e d i n y o ur f i l e s f o r f u t u r er e f e r e n c e .

F o r F u r t h e r I n f o r m a t i o n :N i c h o l a s Panagakos

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VOYAGER

The N a t i o n a l A e r o n a u t i c s a nd S p ac e A d m i n i s t r a t i o n w i l ll a u n c h t w o V oyager s p a c e c r a f t i n l a t e summer 1 9 7 7 f o r a n ex-t e n s i v e r e c o nn a i s s a n ce of t h e o u t e r p l a n e t s .R i d i n g a t o p a T i t a n C e nt a u r r o c k e t , t h e Vo ya ge rs w i l l

be l aunc hed f rom Kennedy Space Ce nt e r , F l a . , on a d e c a d e -l o n g od y ss e y t h a t c o u l d t a k e them t o a s many a s 1 5 majorh e a v e n l y b o d i e s .T he se i n c l u d e g i a n t J u p i t e r and r i n g e d S a t u r n an ds e v e r a l moons o f b o t h p l a n e t s , p r o b a b l y Ur an us a nd p o s s i b l yNeptune.The i n f o r m a t i o n r e t u r n e d by t h e s p a c e c ra f t i s e x p e c t e dt o s h ed new l i g h t on t h e o r i g i n and e a r l y h i s t o r y o f t h es o l a r s y st e m a nd o u r own p l a n e t E a r t h .

Vovaaer Next S t e r , t o S t u dv O u te r P l a n e t sNASA h a s a l r e a d y s e n t s p a c e c r a f t t o V en us , M e rc ur y, J u p i t e rand Mars. P r o j e c t V o y a g e r i s t h e n e x t s t e p i n t h e U n it ed S t a t e sp ro gra m o f s y s t e m a t i c p l a n e t a r y e x p l o r a t i o n i n w hich t h e s o l a rs y s t e m i s u s e d a s a n a t u r a l l a b o r a to r y .The o u t e r r e q i o n of t h e s o l a r s y s t e m i s c o n s i d er e d t h e

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Outer Planets Have Manv S a t e l l i t e sJ u p i t e r and S a t ur n a re d r a s t i c a l l y d i f f e r e n t f r o m t h et e r r e s t r i a l p l a n e t s , a p p e a r i n g t o be composed p r imar i l y o fhydrogen and he l ium . J u p i t e r i s l a r g e r t h a n a l l t h e o t h e rp l a n e t s i n t h e s o l a r s y st e m c om bi ne d. J u p i t e r h a s 1 3 o r 1 4known s a t e l l i t e s ( t h e r e c e n t l y d i sc o v er e d 1 4 t h ha s n o t y e tb ee n c o nf ir m ed ) . J u p i t e r o r b i t s t h e Sun more t ha n f i v e t i m e sf a r t h e r away t h a n E a r t h . One J o v i a n y e a r e q u a l s a b o u t 12E a r th y e a rs . J u p i t e r ' s d ay i s a b o u t 1 0 hour s l ong .S a tu r n o r b i t s t h e Sun almost 1 0 t i m e s a s f a r away a sE a r t h , c o m p l e t in g o n e o r b i t e v e r y 30 E a r t h y e a r s . A day onS a t u r n i s a l s o a bo ut 1 0 h o u r s l on g . T e l e s c o p i c o b s e r v a t i o n so f S a t u r n ' s r i n g s a r e ' d a z z l i n g . The w i d es t v i s i b l er i n g h as a n o u t e r r a d i u s o f 1 3 7 , 0 0 0 k i lom e te r s ( 8 5 , 0 0 0 m i l e s ) .S a t u r n has more t h a n 1 0 s a t e l l i t e s , i n c l u d i n g t h e l a r g e s t ,T i t a n , w hic h h a s a n a tm o s ph e r ic d e n s i t y c om pa ra bl e t o t h a tof E a r t h .

T r a j e c t o r i e s , S pee ds D i f f e rP l a n s c a l l f o r t h e f i r s t l a un ch ed V oyager t o f l y a s l ow e rt r a j e c t o r y , a l l ow i ng t h e s ec on d s p a c e c r a f t -- l aunched abou t12 d a y s l a t e r -- t o o v e r t a k e it a nd r e a c h J u p i t e r a b o u t f o u rmonths e a r l i e r . J u p i t e r ' s g r a v i t y w i l l s l i n g s h o t t h e Voyagersto wa rd t h e r i n g e d p l a n e t S a t u r n , w i t h t h e t w o s p a c e c r a f tr e a c h i n g S a t u r n a b o u t n i n e m on th s a p a r t .Photography of J u p i t e r w i l l b e g i n i n December 1 9 7 8 , 8 0d a ys b e f o r e t h e f i r s t V oyager r e a c h e s t h e p l a n e t . A t t h a tt i m e , images of t h e b r i g h t l y ban ded p l a n e t w i l l a l r e a d y e x c e e d

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P l a n e t s ' Moons t o G e t Close LookS h o r t l y b e f o r e c l o s e s t a pp ro ac h t o J u p i t e r -- on March 5,1 9 7 9 -- Voyager 1 w i l l f l y ab ou t 415,000 km (25 8,000 m i . ) fromAm althea , g i v i n g s c i e n t i s t s t h e i r f i r s t c lo se l o o k a t t h ei nn er m os t o f J u p i t e r ' s s a t e l l i t e s . C l o s e s t a p p r o a c h t o J u p i t e rw i l l b e 3.9 r a d i i ( R J ) from t h e s u r f a c e o f t h e p l a n e t ( a bo u t28 0,00 0 km o r 1 1 0 , 0 0 0 m i . ) . J u p i t e r w i l l o c c u l t t h e Sun an dE a r t h , a s s ee n by i n s t r u m e n t s on t h e s p a c e c r a f t , a l l o w in g

s c i e n t i s t s t o make p r e c i s e m ea s u re m e nt s o f t h e s t r u c t u r e andc o m p o s i t i o n o f i t s a tmosphere .A f t e r pa s s i ng J u p i t e r , t h e f i r s t Voyager w i l l examine a l lf o u r o f t h e b i g G a l i l e a n s a t e l l i t e s : Io f r o m 2 2 , 0 0 0 km ( 1 4 , 0 0 0m i . ) , Eu rop a fro m 733,000 krn ( 4 5 5 , 0 0 0 m i . ) and Ganymede andC a l l i s t o f r o m a b o u t 1 2 0 , 0 0 0 km ( 7 4 , 0 0 0 m i . ) . O b s e r v a t i o n s ofJ u p i t e r w i l l c o n t i n u e f o r a b o u t a month a f t e r c l o s e s t a p p ro ac h ,u n t i l e a r l y A p r i l 1 9 7 9 .The s ec on d Voyager will b e g i n i t s o b s e r v a t o r y p h a s e aboutt w o weeks l a t e r , a g a i n 80 d a y s b e f o r e c l o s e s t approach . I tw i l l o b s e r v e f o u r s a t e l l i t e s d u r i n g t h e i nb ou nd l e g : C a l l i s t ofrom 2 2 0 , 0 0 0 km (1 36, 000 m i , ) , Ganymede from 5 5 ,0 0 0 km (3 4 ,0 0 0m i . ) , Europa f rom 2 0 1 , 0 0 0 km ( 1 2 5 , 0 0 0 m i . ) and Amalthea from5 5 0 ,0 0 0 km (3 42 ,0 00 m i . ) .

E n c o u n t e r s S c h e d u l e dC l o s e s t a pp ro ac h t o J u p i t e r w i l l o c c u r J u l y 1 0 , 1979 .The s p a c e c r a f t , f o l l o w i n g a m o r e d i s t a n t p a t h t ha n i t s p r e -d e c e s s o r , w i l l p a s s 6 4 3 ,0 0 0 km (399,000 m i . ) from t h e c e n t e ro f t h e p l a n e t . The J u p i t e r e n c o u n t e r p e r i o d w i l l c o n t i n u e

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The Voyager spacecraft each weigh 810 kilograms (1,785pounds). The scientific instruments weigh a total of 105 kg(231 lb.) for each spacecraft. The new Voyager spacecraftdiffer from past planetary Mariner spacecraft, due primarilyto the environment into which they will venture and the greatdistance across which they must communicate with Earth. Sincethe outer planets receive only a small fraction of the sunlightthat strikes Earth and Mars, the Voyagers cannot depend onsolar energy but must use nuclear power -- radioisotope thermo-electric generators. Another obvious difference is the largeantenna: the antenna on the Voyager spacecraft is 3.7 meters(12 feet) in diameter.Onboard Instruments Listed

Each Voyager will use 10 instruments and the spacecraftradio to study the planets, their satellites, the rings ofSaturn, the magnetospheres surrounding the planets and inter-planetary space.

In addition to wide-angle and narrow-angle televisioncameras, the Voyagers carry cosmic-ray detectors, infraredspectrometers and radiometers, low-energy charged-particledetectors, magnetometers, photopolarimeters, planetary radio-astronomy instruments, plasma and plasma wave experimentsand ultraviolet spectrometers.The television cameras are expected to provide scientistswith the best pictures of Jupiter and Saturn ever obtained andthe first high-resolution close-up images of the Galileansatellites of Jupiter, the major satellites of Saturn and

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I o , Europa , Ganymede and C a l l i s t o -- J u p i t e r ' s G a l i l e a ns a t e l l i t e s -- and T i t a n q u a l i f y a s o b j e c t s f o r c l o s e s t ud yi n t h e i r own r i g h t . They r a n g e from l a r q e r t ha n t h e p l a n e tMercury down t o t h e s i z e of E a r t h ' s f f o o n ; T i t a n i s t h e o n l ys a t e l l i t e i n t h e s o l a r system known t o h av e a n a p p r e c i a b l ea tm o s p h e r e .The V oy ag er t r a j e c t o r i e s make u s e of t h e f a v o r ab l e o u t e rp l a n e t a l i g n m e n t i d e n t i f i e d d u r i n g p ro p os e d Grand T ou r m i s s i o n

s t u d i e s t o a c h ie v e f l y b y s of b o t h J u p i t e r a nd S a t u rn . Them o s t f a vo r a b l e o p p o r t u n i t y f o r a c l o s e approach t o J u p i t e rw i t h r e l a t i v e l y s h o r t f l i g h t t i m e s t o S a tu r n ( l e s s t h a n f o u ry e a r s ) i s t h e 1977 launch window.The m i s s i o n a l s o b u i l d s on i n f o r m a t i o n g a t h e r e d a b o u tJ u p i t e r by t h e P i o n e e r 1 0 and 11 s p a c e c r a f t -- p a r t i c u l a r l ya b o u t J u p i t e r ' s m a gn et os ph er e.

U r an u s F ly b y O p t io n a lNASA o f f i c i a l s h av e a n o p t i o n t o s e n d t h e second Voyager

The U r a n u s o p t i o n w i l l b e e x e r c i s e d o n ly i fs p a c e c r a f t o n t o t h e p l a n e t U r a n u s , w i t h e n c o u n t er o c c u r r i n gi n J an u ar y 1 9 8 6 .p r im a r y S a t u r n s c i e n c e o b j e c t i v e s h av e be en m e t by t h e f i r s ts p a c e c r a f t and t h e o p e r a t i n g h e a l t h o f t h e s e c o n d w a r r a n t ss u c h a n u n d e r t a k i n g . T h e r e i s a l s o a p o s s i b i l i t y -- b e c a u s eof t h e a l i g n m e n t o f t h e o u t e r p l a n e t s -- t h a t t h e seconds p a c e c r a f t c o u ld be t a r g e t e d t o c o n t i n u e on t o Neptune a f t e ri t s e n c o u n t e r w i t h S a t u r n .

B oth s p a c e c r a f t w i l l e v e n t u a l l y e s c a p e from t h e s o l a r

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The Voyager program is managed by NASA's Office of SpaceScience, Washington, D.C.has been assigned to the Jet Propulsion Laboratory, Pasadena,Calif., which is managed for NASA by the California Instituteof Technology. JPL designed, developed and built the twospacecraft.

Project management responsibility

Launch vehicle responsibility has been assigned to NASA'sLewis Research Center, Cleveland, Ohio. Prime contractors toLewis are Martin Marietta Corp., Denver, Colo. (the Titan),and General Dynamics/Convair, San Diego, Calif. (the Centaur).

Tracking, communications and mission operations are con-ducted by JPL, which operates the Deep Space Network for NASA'sOffice of Tracking and Data Acquisition.The spacecraft's radioisotope thermoelectric generators

are provided to NASA by the Energy Research and DevelopmentAdministration. Prime contractor to ERDA is General Electric.Co., Space Division, Philadelphia, Pa.

Cost of, the Voyager project, exclusive of launch vehiclesand launch operations and tracking and data acquisition, isestimated at $ 3 4 6 million. Launch vehicles for the missionwill cost $71.6 million; and tracking and data acquisition,$32.7 million.

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ExperimentImaging Science

Principal Investigator Instruments and Functions

-.Infrared Interferometer Rudolf HanelSpectrometer Goddard Space FlightCenter

Team Leader, Bradford Smith Two TV cameras with 1,5OOmm, f/8.5University of Arizona, and 200mm, f/2 optics, multipleTucson filters, variable shutter speedsand scan rates. Wide-angle fieldof view, 56 x 55 millirad (about3 degrees square). On scan plat-form.Spectrometer-radiometer measuringtemperatures and molecular gascompositions, with narrow, 1/4-degree field of view, producingmeasurements every 48 seconds; onscan platform.

Ultraviolet Spectrometer A . Lyle BroadfootKitt Peak NationalObservatory

Photopolarimeter

Plasma

Charles LillieUniversity of Colorado

Herbert BridgeMassachusetts Instituteof Technology

Energy Charged Particles S. M. KrimigisJohns Hopkins AppliedPhysics Laboratory

Grating spectrometer measuring ion,abundances; spectral range 400 -atomic, and small-molecular gas I1600 angstroms; on scan platform, I

PI-J

Telescope with variable apertures:filters, polarization analyzers andProof Test Model (PTM) detector; onscan platform.Dual plasma detectors, one alignedtoward Earth/Sun and one perpen-dicular, with detection ranges from4v to 6kv.Dual rotating solid-state detectorsets, covering various ranges from10 kev to more than 30 Mev/nucleon.

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Exper imentC o s m i c Ray

Magnetometer

P l a n e t a r y R a d i oAstronomy

P l a s m a

R ad i o Sc i ence

P r i n c i p a l I n v e s t i g a t o rF. VogtC a l i f o rn i a I n s t i t u t e of

Technology

I n s t r u m e n t s a n d F u n c t i o n sHigh-energy, low-energy ande l e c t r o n t e l e s c o p e s y s te m s u s i n ga r r a y s o f s o l i d - s t a t e d e t e c t o r s ,s e v e r a l ra n g e s f ro m 0 . 1 5 t o 50 0Mev/nucleon.

Norman N e s s Two low-f i e l d t r i a x i a l f l u x g a t eG odda rd Space F l i g h t C en t e r m agnet om e te r s l o ca t e d r ou gh l y 10m(33 ft.) f rom sp ac ec r a f t on boom ,t w o h i gh - f i e l d ( 2 0 g a u s s ) i n s t r u -m ent s m ount ed on spa ce c r a f t .J a m e s WarwickU n i v e r s i t y o f C o lo r a d o

F r e d e r i c k L. S c a r fTRW Systems Group

TWO 1 0 -m ( 33 - f t . ) w h ip an t e nnas andtwo-band receiver (20.4-1300 kHz,2.3-40.5 MHz) , d e t e c t i n g p l a n e t a r yr a d i o e m is s i o n s an d b u r s t s a n ds o l a r / s t e l l a r b u r s t s .U s e s 10 -m ( 3 3 - ft . ) p l a n e t a r y r a d i oa s t r o n m i y a n t e n n a s w i t h s t e p If r equency de t e c t o r and w avef or ma n a l y z e r t o m e a su r e p la s ma w a v e s ,t h e rm a l pl as ma d e n s i t y p r o f i l e a tJ u p i t e r a n d S a t u r n , s a t e l l i t e /m a g n et o sp h e re i n t e r a c t i o n s , w av e/p a r t i c l e i n t e r a c t i o ns .

I

T e a m Leader , Von R. Eshleman Uses spacecraf t S-band/X-bandS t a n f o r d U n i v e r s i t y l i n k s d u r i n g p l a n e t , s a t e l l i t eand Sa t u r n r i n g o c c u l t a t i o n s t op e r c e i v e c h an g es i n r e f r a c t i v i t ya n d a b s o r p t i o n ; c e l e s t i a l m echan i c si n f o r m a ti o n c a l c u l a t e d fro mt r a c k i n g d a t a .-end-